System and method for managing accumulator effects during engagement of a lockup clutch in a torque converter

ABSTRACT

A dynamic model that is configured to produce a lockup clutch command as a function of a plurality of torque converter operating parameters is continually solved and the lockup clutch command is asserted to control engagement of the lockup clutch. A profile of one of the plurality of torque converter operating parameters is selected and is configured, when inserted into the model in place of an actual value thereof, to result in an intersection of rotational speeds of the pump and the turbine over time. Deceleration of the pump is monitored after asserting the lockup clutch command and a maximum deceleration of the pump is determined therefrom. The selected profile is temporarily held constant if the monitored deceleration of the pump rises at least a threshold value above the maximum deceleration of the pump.

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims priority to, and the benefit of, U.S.Provisional Patent Application No. 61/045,129 filed Apr. 15, 2008, thedisclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to torque converters that serveas interfaces between internal combustion engines and automatictransmissions in mobile vehicles, and more specifically to the controlof lockup clutches in such torque converters.

BACKGROUND

Torque converters are commonly used as an interface between an internalcombustion engine and a transmission having a number of automaticallyselectable gear ratios. Some torque converters include a so-calledlockup clutch that is connected between the pump and turbine of thetorque converter, and that is engaged under certain operating conditionsto rigidly connect the pump and turbine together. It is desirable tomanage accumulator effects that may occur when controlling engagement ofthe lockup clutch.

SUMMARY

The present invention may comprise one or more of the features recitedin the attached claims, and/or one or more of the following features andcombinations thereof. In a torque converter having a pump that isrotatably driven by an internal combustion engine and that is fluidlycoupled to a turbine, and a lockup clutch connected between pump and theturbine, a method for managing accumulator effects during engagement ofthe lockup clutch may comprise continually solving a dynamic model thatis configured to produce a lockup clutch command as a function of aplurality of torque converter operating parameters, asserting the lockupclutch command to control engagement the lockup clutch, selecting aprofile of one of the plurality of torque converter operating parametersthat is configured, when inserted into the model in place of an actualvalue thereof, to result in an intersection of rotational speeds of thepump and the turbine over time, monitoring deceleration of the pumpafter asserting the lockup clutch command, determining from monitoredvalues of the deceleration the pump a maximum deceleration of the pump,and temporarily holding constant the selected profile if the monitoreddeceleration of the pump rises at least a threshold value above themaximum deceleration of the pump.

Temporarily holding constant the selected profile may comprise holdingthe selected profile at a constant value for a predefined time periodfollowing detection of the monitored deceleration of the pump rising atleast the threshold value above the maximum deceleration of the pump.

The method may further comprise monitoring a number of the remainingones of the plurality of torque converter operating parameters, andcontinually solving the dynamic model using the monitored values of thenumber of the remaining ones of the plurality of torque converteroperating parameters and the profile of the one of the plurality oftorque converter operating parameters. The lockup clutch command maycomprise a fill phase followed by an initial lockup clutch activationvalue after which on-coming capacity of the lockup clutch occurs. Thelockup clutch command produced by the model may be used to controlengagement of the lockup clutch only after the on-coming capacity of thelockup clutch occurs. Monitoring a number of the remaining ones of theplurality of torque converter operating parameters, selecting a profile,continually solving the dynamic model using the monitored values of thenumber of the remaining ones of the plurality of torque converteroperating parameters and the profile of the one of the plurality oftorque converter operating parameters, monitoring deceleration of thepump, determining a maximum deceleration of the pump and temporarilyholding constant the selected profile may all carried out afteron-coming capacity of the lockup clutch occurs.

One of the plurality of torque converter operating parameters that maybe included in the model is the inertia of the engine. Selecting aprofile may comprise selecting a pump speed profile and computing a pumpacceleration profile as a function thereof, the pump speed profile beingconfigured to decrease the rotational speed of the pump from arotational speed at or just after on-coming capacity of the lockupclutch occurs to the rotational speed of the turbine over time.Monitoring a number of the remaining ones of the plurality of torqueconverter operating parameters may comprise monitoring torque applied bythe engine to the pump and monitoring rotational speed of the turbine.The model may define the lockup clutch command as a function of theinertia of the engine, the torque applied by the engine to the pump, therotational speed of the turbine, the pump speed profile and the pumpacceleration profile. Monitoring torque applied by the engine to thepump may comprise receiving reported engine output torque valuesproduced by a controller configured to control operation of the internalcombustion engine. In one example embodiment, the method may furthercomprise determining torque transmitted by the pump as a function of thepump speed profile and the rotational speed of the turbine, and thedynamic model may define the lockup clutch command according to theequation: T_(LU)=T_(E)−T_(P)−(I_(E)*PAP), where T_(LU) is the lockupclutch command, T_(E) is the torque applied by the engine to the pump,T_(P) is the torque transmitted by the pump, I_(E) is the inertia of theengine and PAP is the pump acceleration profile. In another exampleembodiment, monitoring torque applied by the engine to the pump maycomprise determining an initial rotational speed of the pump during thefill phase of the lockup clutch command, determining an initialrotational speed of the turbine during the fill phase of the lockupclutch command, receiving an initial value of a reported engine outputtorque produced by a controller during the fill phase of the lockupclutch command, determining a torque offset value as a function of theinitial rotational speeds of the pump and the turbine, and the initialvalue of the reported engine output torque, receiving reported engineoutput torque values after on-coming capacity of the lockup clutchoccurs, the reported engine output torque values produced by acontroller configured to control operation of the internal combustionengine controller, and computing the torque applied by the engine to thepump as a compensated engine output torque based on the torque offsetvalue and the reported engine output torque values produced by thecontroller after on-coming capacity of the lockup clutch occurs. In thisexample embodiment, the method may further comprise determining torquetransmitted by the pump as a function of the pump speed profile and therotational speed of the turbine, and the dynamic model may define thelockup clutch command according to the equation:T_(LU)=T_(EC)−T_(P)−(I_(E)*PAP), where T_(LU) is the lockup clutchcommand, T_(EC) is the compensated engine output torque, T_(P) is thetorque transmitted by the pump, I_(E) is the inertia of the engine andPAP is the pump acceleration profile.

The lockup clutch command may be a pressure command to which a lockupclutch actuator is responsive to control operating pressure of thelockup clutch.

In one example embodiment, selecting a profile of one of the pluralityof torque converter operating parameters may comprise selecting a linearprofile of the one of the plurality of torque converter operatingparameters, and selecting a change rate corresponding to a rate ofchange of the selected linear profile over time. In another exampleembodiment, selecting a profile of one of the plurality of torqueconverter operating parameters may comprise selecting a non-linearprofile of the one of the plurality of torque converter operatingparameters, and selecting a change rate corresponding to a rate ofchange of the selected non-linear profile over time. In yet anotherexample embodiment, selecting a profile of one of the plurality oftorque converter operating parameters may comprise selecting a pumpspeed profile that is configured to decrease the rotational speed of thepump from a rotational speed at or just after on-coming capacity of thelockup clutch occurs to the rotational speed of the turbine over time,and selecting a decay rate corresponding to a rate of decay of theselected pump speed profile over time. In yet a further exampleembodiment, selecting a profile of one of the plurality of torqueconverter operating parameters may comprise selecting a turbine speedprofile that is configured to increase the rotational speed of theturbine from a rotational speed at or just after on-coming capacity ofthe lockup clutch occurs to the rotational speed of the pump over time,and selecting an increase rate corresponding to a rate of increase ofthe selected turbine speed profile over time.

In a torque converter having a pump that is rotatably driven by aninternal combustion engine and that is fluidly coupled to a turbine, anda lockup clutch connected between the pump and the turbine, a method formanaging accumulator effects during engagement of the lockup clutch maycomprise determining inertia of the engine, determining torque appliedby the engine to the pump, determining rotational speed of the turbine,selecting a pump speed profile that reduces rotational speed of the pumpfrom a first speed to the rotational speed of the turbine, determining apump acceleration profile based on the pump speed profile, controllingengagement of the lockup clutch as a function of the inertia of theengine, the torque applied by the engine to the pump, the rotationalspeed of the turbine, the pump speed profile and the pump accelerationprofile, monitoring deceleration of the pump, determining from monitoredvalues of the deceleration the pump a maximum deceleration of the pump,and temporarily holding constant the pump speed profile if the monitoreddeceleration of the pump rises at least a threshold value above themaximum deceleration of the pump.

Controlling engagement of the lockup clutch may comprise computing alockup clutch command using a dynamic model that defines the lockupclutch as a function of the inertia of the engine, the torque applied bythe engine to the pump, the rotational speed of the turbine, the pumpspeed profile and the pump acceleration profile, and controllingengagement of the lockup clutch using the lockup clutch command. Thelockup clutch command may comprise a fill phase followed by an initiallockup clutch activation value after which on-coming capacity of thelockup clutch occurs. The lockup clutch command produced by the modelmay be used to control engagement of the lockup clutch only after theon-coming capacity of the lockup clutch occurs. The lockup clutchcommand may comprise a fill phase followed by an initial lockup clutchactivation value. Lockup clutch on-coming capacity may be detected when,following assertion of the initial lockup clutch activation value,torque transmitted by the lockup clutch exceeds a torque threshold. Thefirst speed of the pump speed profile may correspond to a rotationalspeed of the pump when or just after the lockup clutch on-comingcapacity is detected.

Temporarily holding constant the selected profile may comprise holdingthe selected profile at a constant value for a predefined time periodfollowing detection of the monitored deceleration of the pump rising atleast the threshold value above the maximum deceleration of the pump.

A system for managing accumulator effects during engagement of a lockupclutch in a torque converter may comprise a turbine, a pump engaging anoutput shaft of an internal combustion engine and fluidly coupled to theturbine, wherein the lockup clutch is connected between the pump and theturbine, a first sensor configured to produce a pump speed signalcorresponding to a rotational speed of the pump, a second sensorconfigured to produce a turbine speed signal corresponding to arotational speed of the turbine, and a control circuit. The controlcircuit may include a memory having instructions stored therein that areexecutable by the control circuit to compute a pump speed profile thatreduces rotational speed of the pump from a first speed to therotational speed of the turbine, to compute a pump acceleration profilebased on the pump speed profile, to compute a lockup clutch command as afunction of the inertia of the engine, the torque applied by the engineto the pump, the rotational speed of the turbine, the pump speed profileand the pump acceleration profile, to control engagement of the lockupclutch using the lockup clutch command, to monitor pump deceleration asa function of the pump speed signal, to determine a maximum pumpdeceleration as a function of monitored values of the pump deceleration,and to temporarily hold constant the pump speed profile if the monitoreddeceleration of the pump rises at least a threshold value above themaximum deceleration of the pump.

The system may further comprise an actuator configured to be responsiveto the lockup clutch command to control engagement of the lockup clutch.The control circuit may be configured to produce the lockup clutchcommand.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram and schematic view of one illustrativeembodiment of a system for controlling operation of a lock up clutch ina torque converter.

FIG. 2 is a flowchart of one illustrative embodiment of a process forcontrolling lock up clutch operation.

FIG. 3 is a plot of a number of operating parameters associated withlock up clutch operation.

FIG. 4 is a flowchart of one illustrative embodiment of a process fordetecting lockup clutch on-coming capacity.

FIG. 5 is a flowchart of one illustrative embodiment of a process forcontrolling engagement of the lock up clutch following detection oflockup clutch on-coming capacity.

FIG. 6 is a flowchart of one illustrative embodiment of a process fordetermining pump shaft speed and acceleration profiles for use with theprocess of FIG. 5.

FIG. 7 is a flowchart of one illustrative embodiment of a process formanaging accumulator effects during the process of FIG. 5.

FIG. 8 is a plot of a number of operating parameters associated withlock up clutch operation during the accumulator management process ofFIG. 7.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to a number of illustrativeembodiments shown in the attached drawings and specific language will beused to describe the same.

Referring now to FIG. 1, a block diagram and schematic view of oneillustrative embodiment of a system 10 for controlling operation of alock up clutch in a torque converter is shown. In the illustratedembodiment, the system 10 includes an internal combustion engine 12 thatis configured to rotatably drive an output shaft 14 that is coupled toan input or pump shaft 16 of a conventional torque converter 20. Theinput or pump shaft 16 is attached to an impeller or pump 18 that isrotatably driven by the output shaft 14 of the engine 12. The torqueconverter 20 further includes a turbine 22 that is attached to a turbineshaft 24, and the turbine shaft 24 is coupled to, or integral with, arotatable input shaft 26 of a transmission 28. The transmission 28 isconventional and includes a number of automatically selected gearratios. An output shaft 30 of the transmission is coupled to, androtatably drives, a number of wheels (not shown) of a vehicle carryingthe engine 12, torque converter 20 and transmission 28.

A conventional lockup clutch 32 is connected between the pump 18 and theturbine 22, and the lockup clutch 32 is fluidly coupled to a fluidactuator 36 via a fluid passageway 34. The operation of the torqueconverter 20 is conventional in that the torque converter 20 is operablein a so-called “torque converter” mode during certain operatingconditions such as vehicle launch, low speed and certain gear shiftingconditions. In the torque converter mode, the lockup clutch 32 isdisengaged and the pump 18 rotates at the rotational speed of the engineoutput shaft 14 while the turbine 22 is rotatably actuated by the pump18 through a fluid (not shown) interposed between the pump 18 and theturbine 22. In this operational mode, torque multiplication occursthrough the fluid coupling such that the turbine shaft 24 is exposed tomore drive torque than is being supplied by the engine 12, as is knownin the art. The torque converter 20 is alternatively operable in aso-called “lockup” mode during other operating conditions, such as whencertain gear ratios of the transmission 28 are engaged. In the lockupmode, the lockup clutch 32 is engaged and the pump 18 is thereby securedto directly to the turbine 22 so that the engine output shaft 14 isdirectly coupled to the input shaft 26 of the transmission 28, as isalso known in the art.

The system 10 further includes a transmission control circuit 40 thatincludes a memory unit 42 and a conventional timer circuit 44. Thetransmission control circuit 40 is illustratively microprocessor-based,and the memory unit 42 generally includes instructions stored thereinthat are executable by the transmission control circuit 40 to controloperation of the torque converter 20 and the transmission 28. It will beunderstood, however, that this disclosure contemplates other embodimentsin which the transmission control circuit 40 is notmicroprocessor-based, but is configured to control operation of thetorque converter 20 and/or transmission 28 based on one or more sets ofhardwired instructions and/or software instructions stored in the memoryunit 42.

In the system 10 illustrated in FIG. 1, the torque converter 20 and thetransmission 28 each include one or more sensors configured to producesensor signals that are indicative of one or more operating states ofthe torque converter 20 and/or the transmission 28. For example, thetorque converter 20 includes the conventional speed sensor 50 that ispositioned and configured to produce a speed signal corresponding to therotational speed of the torque converter pump shaft 16 (which is alsothe rotational speed of the output shaft 14 of the engine 12). The speedsensor 50 is electrically connected to a pump speed input, PS, of thetransmission control circuit 40 via a signal path 52, and thetransmission control circuit 40 is operable to process the speed signalproduced by the speed sensor 50 in a conventional manner to determinethe rotational speed of the pump shaft 16. The transmission 28 furtherincludes a second speed sensor 54 that is positioned and configured toproduce a speed signal corresponding to the rotational speed of theinput shaft 26 of the transmission 28. The input shaft 26 of thetransmission 28 is directly coupled to, or integral with, the turbineshaft 24, and the speed sensor 54 may alternatively be positioned andconfigured to produce a speed signal corresponding to the rotationalspeed of the turbine shaft 24. In any case, the speed sensor 54 may beconventional, and is electrically connected to a turbine speed input,TS, of the transmission control circuit 40 via a signal path 56. Thetransmission control circuit 40 is configured to process the speedsignal produced by the speed signal 54 in a conventional manner todetermine the rotational speed of the turbine shaft 24/input shaft 26 ofthe transmission 28.

In the illustrated embodiment, the transmission 28 further includes oneor more actuators configured to control various operations within thetorque converter 20 and/or transmission 28. For example, thetransmission 28 includes an actuator 36 that is electrically connectedto a lockup clutch command output, LCC, of the transmission controlcircuit 40 via a signal path 62. The actuator 36 is responsive to thelockup clutch command signal, LCC, produced by the transmission controlcircuit 40 on the signal path 62 to control the pressure of fluid withinthe fluid passageway 34, and thus the actuating pressure supplied to thelockup clutch 32. Illustratively, the actuator 36 may be provided in theform of a conventional charge pump fluidly coupled to a source of fluid,e.g., transmission oil, although this disclosure contemplates otherembodiment in which the actuator may alternatively be provided in theform of a conventional valve, pump or the like, that is fluidly coupledto a source of fluid, e.g., transmission oil.

In the illustrated embodiment, the system 10 further includes an enginecontrol circuit 66 having an input/output port (I/O) that iselectrically coupled to the engine 12 via a number, M, of signal paths,wherein M may be any positive integer. The engine control circuit 66 maybe conventional, and is operable to control and manage the overalloperation of the engine 12. The engine control circuit 66 furtherincludes a communication port, COM, that is electrically connected to asimilar communication port, COM, of the transmission control circuit 40via a number, N, of signal paths 64, wherein N may be any positiveinteger. The one or more signal paths 64 are typically referred tocollectively as a data link. Generally, the engine control circuit 66and the transmission control circuit 40 are operable to shareinformation via the one or more signal paths 64 in a conventionalmanner. In one embodiment, for example, the engine control circuit 66and transmission control circuit 40 are operable to share informationvia the one or more signal paths 64 in the form of one or more messagesaccordance with a society of automotive engineers (SAE) J-1939communications protocol, although this disclosure contemplates otherembodiments in which the engine control circuit 66 and the transmissioncontrol circuit 40 are operable to share information via the one or moresignal paths 64 in accordance with one or more other conventionalcommunication protocols.

As it relates to this disclosure, the transmission control circuit 40 isoperable to receive certain operating information relating to operationof the engine 12 from the engine control circuit 66 via the one or moresignal paths 64 in a conventional manner. For example, the enginecontrol circuit 66 is configured in a conventional manner to determinethe instantaneous output torque produced by the engine 12, and in theillustrated embodiment the engine control circuit 66 is operable tosupply the instantaneous engine output torque information to thetransmission control circuit 40 via the one or more signal paths 64,such as in the form of a message that the transmission control circuit40 may process to determine a corresponding engine output torque value.As another example, the engine control circuit 66 is operable in aconventional manner to determine the rotational speed of the engineoutput shaft 14, and in one embodiment the engine control circuit 66 isoperable to supply the engine rotational speed information to thetransmission control circuit 40 via the one or more signal paths 64. Inthis embodiment, the speed sensor 50 described hereinabove is notnecessary, and may be omitted or otherwise be unused. Alternatively, thetransmission control circuit 40 may be configured to determine therotational speed of the engine 12 using both the signal produced by thesensor 50 and the engine rotational speed information supplied by theengine control circuit 66 via the one more signal paths 64.

Referring now to FIG. 2, a flow chart is shown of one illustrativeembodiment of a process 100 for controlling operation of the lockupclutch 32. The process 100 is illustratively stored in the memory unit42 of the transmission control circuit 40 in the form of one or moresets of instructions that are executable by the transmission controlcircuit 40 to control operation of the lockup clutch 42. The process 100will be described with the aid of the plot of FIG. 3, which shows anumber of operating parameters (arbitrary scale) over time (seconds). Inparticular, the plot of FIG. 3 shows engine output torque 120 (e.g.,supplied to the transmission control circuit 40 by the engine controlcircuit 66), engine (pump shaft) speed 122 (e.g., produced by the speedsensor 50), turbine speed 126 (e.g., produced by the speed sensor 54)and lockup clutch pressure 128 (e.g., produced by the pressure sensor58). Other signals and/or features are also shown in the plot of FIG. 3,and such other signals and/or signal features will be describedhereinafter within the context of the process 100.

The process 100 begins at step 102, and thereafter at step 104 thetransmission control circuit 40 is operable to determine if the lockupclutch command, LCC, has been asserted, i.e., is active. In theillustrated embodiment, the transmission control circuit 40 is operableto produce the lockup clutch command, LCC, according to one or more setsof instructions stored in the memory 42, and therefore has knowledge ofthe state of the lockup clutch command, LCC. If the transmission controlcircuit 40 determines at step 104 that the lockup clutch command, LCC,has not been asserted, the process 100 loops back to step 104. If, onthe other hand, the transmission control circuit 40 determines at step104 that the lockup clutch command, LCC, has been asserted, execution ofthe process 100 advances to step 106 where the transmission controlcircuit 40 is operable to determine initial pump and turbine shaftrotational speeds, PS_(i) and TSi, and initial engine output torque,T_(Ei) during the fill phase of the lockup clutch command, LCC.

Referring to FIG. 3, lockup clutch pressure is represented by thewaveform 128, and the lockup clutch pressure 128 generally follows thelockup clutch command, LCC. The wave form 128 thus represents the lockupclutch command, LCC, and the waveform 128 will be used herein toillustrate and described the operation of LCC. In any case, the lockupclutch command 128 illustrated in FIG. 3 includes a conventional fillphase followed by a controlled pressure increase until engagement of thelockup clutch 32 is achieved. The fill phase of the lockup clutchcommand 128 follows assertion of the lockup clutch command, and isidentified by a rapid increase to a peak pressure 130 for a shortduration followed by a rapid decrease in pressure to an initial pressurevalue or initial lockup clutch activation value 132. The fill phase isused in a conventional manner to cause the piston (not shown) of thelockup clutch 32 to travel rapidly toward, but not contact, a pistonstop (not shown) defined by the lockup clutch 32 under high fluidpressure conditions. Following the fill phase, the lockup clutchpressure 128 is then controllably increased from the initial pressurevalue or initial lockup clutch activation value 132 to achieveengagement of the lockup clutch 32.

Referring again to FIG. 2, the transmission control circuit 40 isillustratively operable at step 106 to determine the initial pump shaftrotational speed TS_(i), by monitoring the speed signal produced by thespeed sensor 50. Alternatively or additionally, the transmission controlcircuit 40 may be operable at step 106 to determine the pump shaftrotational speed PS_(i), based on engine rotational speed informationsupplied by the engine control circuit 66 to the transmission controlcircuit 40 via the one or more signal paths 64. The transmission controlcircuit 40 is illustratively operable at step 106 to determine theturbine shaft rotational speed, TS_(i), by monitoring the speed signalproduced by the speed sensor 54. The transmission control circuit 40 isfurther illustratively operable at step 106 to determine the initialengine output torque value T_(Ei), by receiving the engine output torqueinformation supplied by the engine control circuit 66 on the one or moresignal paths 64. Illustratively, the transmission control circuit 40 isoperable to determine PS_(i), TS_(i) and T_(Ei), during an initialportion of the fill phase, e.g., just after the peak pressure 130 isachieved, although this disclosure contemplates alternate embodiments inwhich the transmission control circuit 40 is operable to determinePS_(i), TS_(i) and T_(Ei), during one or more other portions of the fillphase, and/or during one or more other portions of the lockup clutchcommand, LCC, that follow the fill phase.

Following step 106, the transmission control circuit 40 is operable atstep 108 to compute an initial pump shaft torque, T_(Pi), as a functionof the initial pump and turbine shaft rotational speed values, PS_(i)and TS_(i) respectively. In one embodiment, the transmission controlcircuit 40 is operable to compute the initial pump shaft torque value,T_(Pi) according to the formula T_(Pi)=a*PS_(i)²+b*PS_(i)*TS_(i)+c*TS_(i) ², although the transmission control circuit40 may be alternatively operable at step 108 to compute the initial pumpshaft torque value T_(Pi) using one or more other conventional functionsof PS_(i) and TS_(i) or as functions of more, fewer and/or differenttorque converter 20 and/or transmission 28 operating parameters. In anycase, the process 100 advances from step 108 to step 110 where thetransmission control circuit 40 is operable to compute an engine outputtorque offset value, ΔT_(i) according to the equationΔT_(i)=T_(Pi)−T_(Ei).

Following step 110, the control circuit 40 is operable at step 112 todetermine whether the fill phase of the lockup clutch command, LCC iscomplete and an initial LCC value has been asserted. Illustratively, thetransmission control circuit 40 is operable to execute step 112 bymonitoring the lockup clutch command, LCC, and to determine that thefill phase of the lockup clutch command is complete when the lockupclutch command, e.g., lockup clutch pressure command or other lockupclutch command from which lockup clutch pressure may be determined,drops from the peak fill phase pressure 130 to the initial pressurevalue or initial lockup clutch activation (LCC) value. If thetransmission control circuit 40 determines that the fill phase of thelockup clutch command is not complete, the process 100 loops back tostep 112. If, on the other hand, the transmission control circuit 40determines at step 112 at the fill phase of LCC is complete and theinitial LCC value has been asserted, the process 100 advances to step114 where the transmission control circuit executes a lockup clutchoncoming capacity detection routine.

Referring now to FIG. 4, one illustrative embodiment of the lockupclutch oncoming capacity detection routine 114 is shown. The lockupclutch oncoming capacity detection routine 114 begins at step 150 wherethe transmission control circuit 40 is operable to determine an engineinertia value, I_(E), corresponding to an inertia associated with theengine 12. Illustratively, the engine inertia value, I_(E), is stored inthe memory unit 42, and the transmission control circuit 40 is operableto determine the engine inertia value I_(E), at step 150 by retrievingI_(E) from the memory unit 42. Alternatively, the engine inertia value,I_(E), may be provided to the transmission control circuit 40 by theengine control circuit 66 via the one or more signal paths 64, such asin the form of a message that may be processed by the transmissioncontrol circuit 40 to determine the engine inertia value. Alternativelystill, the transmission control circuit 40 may be operable at step 150to compute the engine inertia value, I_(E), based on one or more engineoperating parameters supplied to the transmission control circuit 40 bythe engine control circuit 66 via the one or more signal paths 64.Further alternatively, the engine control circuit 66 may be operable tocompute the engine inertia value, I_(E), based on one or more engineoperating parameters, and to supply the engine inertia value, I_(E), tothe transmission control circuit 40 at step 150 via the one or moresignal paths 64. In any case, the lockup clutch oncoming capacitydetection routine advances from step 150 to step 152 where thetransmission control circuit 40 is operable to determine an engineoutput torque value, T_(E), corresponding to the output torque producedby the engine 12. Illustratively, the engine output torque value, T_(E),corresponds to an instantaneous value of the engine output torque, andis supplied at step 152 to the transmission control circuit 40 by theengine control circuit 66 via the one or more signal paths 64 asdescribed hereinabove.

Following step 152, the transmission control circuit 40 is operable atstep 154 to compute a compensated engine output torque value, T_(EC), asa function of the instantaneous engine output torque value, T_(E), andthe engine output torque offset value, ΔT_(i), which was computed atstep 110 of the process 100 (see FIG. 2). This embodiment presumes thatany inaccuracies in the engine output torque values, T_(E), supplied bythe engine control circuit 66 are uniform across all engine outputtorque values so that compensating engine output torque values, T_(E),using the engine output torque offset value, ΔT_(i), effectivelyremoves, or at least reduces, such inaccuracies across all engine outputtorque values within typical engine output torque ranges. Conversely, inembodiments in which the engine output torque value, T_(E), produced bythe engine control circuit 66 and supplied by the transmission controlcircuit 40 via the one or more signal paths 64 accurately reflects, orreflects within an acceptable error, the actual torque applied to thepump shaft 16 of the torque converter 20, step 110 of the process 100and step 154 of the routine 114 may be omitted. In this case, the engineoutput torque values, T_(E), supplied by the engine control circuit 66to the transmission control circuit 40 via the one or more signal paths64 may be used by the routine 114. In another alternative embodiment,step 110 of the process 100 and step 154 of the routine 114 may beomitted, and the transmission control circuit 40 may be operable at step152 to determine the engine output torque, T_(E), by estimating thetorque applied to the pump shaft 16 of the torque converter 20 accordingto one or more conventional engine output torque models.

The routine 114 advances from step 154 to step 156 where thetransmission control circuit 40 is operable to determine the pump shaftrotational speed, PS, corresponding to the rotational speed of the pumpshaft 16 of the torque converter 20. The pump shaft rotational speed,PS, may be determined at step 156 by the transmission control circuit 40as described hereinabove with respect to step 106 of the process 100.Following step 156, the transmission control circuit 40 is operable atstep 158 to compute a pump shaft angular acceleration value, PA, as afunction of the pump shaft rotational speed, PS, which was determined atstep 156. Thereafter at step 160, the transmission control circuit 40 isoperable to determine a turbine shaft rotational speed, TS,corresponding to a rotational speed of the turbine shaft 24 of thetorque converter 20. The transmission control circuit 40 isillustratively operable to execute step 160 using any one or more of thetechniques described hereinabove with respect to step 106 of the process100.

Following step 160, the routine 114 advances to step 162 where thetransmission control circuit 40 is operable to compute a lockup clutchtorque value, T_(LU), as a function of I_(E), T_(EC), PS, PA and TS. Inone illustrative embodiment, for example, the transmission controlcircuit 40 is operable to execute step 162 by computing T_(LU) accordingto the model: T_(LU)=T_(EC)−T_(P)−(I_(E)*PA), where T_(P) represents theamount of torque transmitted by the pump 18 of the torque converter 20.Illustratively, T_(P) is computed by the transmission control circuit 40as a function of PS and TS using a model-based transmitted torque modelsuch as, but not limited to, that is described hereinabove with respectto step 108 of the process 100. Alternatively, such as in embodiments inwhich the engine output torque value, T_(E), supplied by the enginecontrol circuit 66 to the transmission control circuit 40 via one ormore of the signal paths 64 is not compensated, the transmission controlcircuit 40 may be operable to determine the lockup clutch torque value,T_(LU), according to the model: T_(LU)=T_(E)−T_(P)−(I_(E)*PA), whereT_(E) represents an uncompensated value of the engine output torque thatmay be determined according to any one or more of the techniquesdescribed hereinabove. In any case, the lockup clutch torque value,T_(LU), computed at step 162 represents an estimate, based on measuredand/or estimated operating values, of the actual torque beingtransmitted by the lockup clutch 32 over time. As it relates to the plotof FIG. 3, the lockup clutch torque estimate, T_(LU), computed at step162 corresponds to the torque being transmitted by the lockup clutch 32during the initial portion of the lockup clutch pressure 128 that occursafter the fill phase and after the initial pressure or initial lockupclutch activation value 132 is asserted. Illustratively, the T_(LU)model is stored in the memory unit 42 of the transmission controlcircuit 40, and the transmission control circuit 40 is operable at step162 to retrieve the T_(LU) model from the memory unit 42, to insertcurrent values of the torque converter operating parameters I_(E),T_(EC) (or T_(E)), PS, PA and TS into the model and to then solve themodel equation for T_(LU).

The routine 114 advances from step 162 to step 164 where thetransmission control circuit 40 is operable to determine whether thelockup clutch torque value, T_(LU), that was computed at step 162 isgreater than a threshold torque value, T_(TH). If not, execution of theroutine 114 loops back to step 152. If, on the other hand, thetransmission control circuit 40 determines at step 164 that the lockupclutch torque value T_(LU) is greater than the threshold torque valueT_(TH), execution of the routine 114 advances to step 166 where thetransmission control circuit 40 is operable to produce a lockup clutchon-coming capacity signal. As used herein, the term “on-coming clutchcapacity” is defined as a condition in which the clutch in question,here the lockup clutch 32, is sufficiently engaged to transmit adiscernable amount of torque. In this regard, the torque threshold,T_(TH), illustratively corresponds to a threshold torque above which thelockup clutch 32 is transmitting a discernable amount of torque. In anycase, the transmission control circuit 40 may be configured to producethe lockup clutch on-coming capacity signal at step 166 by providing acorresponding lockup clutch on-coming capacity value to one or morecontrol algorithms that are being executed by, or that may be executedby, the transmission control circuit 40, by storing a lockup clutchon-coming capacity value in one or more locations in the memory unit 42,by supplying a lockup clutch on-coming capacity signal to the enginecontrol circuit 66 via the one or more signal paths 64, or the like. Inany case, execution of the routine 114 advances from step 166 to step168 where the routine 114 is returned to step routine 114 to the process100 of FIG. 2.

Referring again to FIG. 3, the pump shaft speed 122 generally decreaseswhen engagement of the lockup clutch 32 is being commanded. As the pumpshaft speed 122 decreases toward the turbine speed 126 following thefill phase of the lockup clutch command 128 and subsequent assertion ofthe initial pressure value or initial lockup clutch activation value132, the torque transmitted by the lockup clutch 32 will increaseslightly over time until the lockup clutch 32 begins to transmit adiscernable amount of torque. This point in time is identified in FIG. 3as 134, and corresponds to the point in time, following the fill phaseof the lockup clutch command 128 at which the torque transmitted by thelockup clutch 32 is greater than T_(TH). It is at this point that lockupclutch on-coming capacity is detected. The process illustrated in FIG. 4is operable as just described to continually estimate the lockup clutchtorque, T_(LU), by continually solving the above lockup clutch torquemodel, and to detect lockup clutch on-coming capacity when the estimatedlockup clutch torque, T_(LU), exceeds the torque threshold, T_(TH).

Referring again to FIG. 2, the process 100 advances from step 114 tostep 116 where the transmission control circuit 40 is operable toexecute a lockup clutch control routine. Referring now to FIG. 5, oneillustrative embodiment of the lockup clutch control routine 116 isshown. In the illustrated embodiment, the lockup clutch control routine116 begins at step 180 where the transmission control circuit 40 isoperable to hold the timer 44 (see FIG. 1) in reset. Thereafter at step182, the transmission control circuit 40 is operable to set a countervalue, K, equal to one. Thereafter at step 184, the transmission controlcircuit 40 is operable to execute a pump shaft speed and an accelerationprofile determination routine.

Referring to FIG. 6, one illustrative embodiment of the pump shaft speedand acceleration profile determination routine 184 is shown. In theillustrated embodiment, the pump shaft speed and acceleration profiledetermination routine 184 begins at step 210 where the transmissioncontrol circuit 40 is operable to determine a pump shaft rotationalspeed value, PS_(C), corresponding to the rotational speed of the pump16 of the torque converter 20 at, or just after, detection of on-comingcapacity of the lockup clutch 32 as determined by the lockup clutchon-coming capacity detection routine 114 of FIG. 4. In the plot of FIG.3, for example, the pump shaft rotational speed, PS_(C), is identifiedby the intersection of the dashed vertical line 134 with the pump speedwaveform 122. Following step 210, the transmission control circuit 40 isoperable at step 212 to determine the turbine shaft rotational speed,TS, corresponding to the rotational speed of the turbine shaft 24 of thetorque converter 20 at, or just after, detection of on-coming capacityof the lockup clutch 32. Illustratively, the transmission controlcircuit 40 is operable to determine the pump shaft rotational speed,PS_(C), and the turbine shaft rotational speed, TS, using any of thetechniques described hereinabove.

Following step 212, the transmission control circuit 40 is operable atstep 214 to select a pump speed profile, PSP, and to determine a pumpspeed profile decay rate, DR, as a function of PS_(C), TS and PSP.Illustratively, the pump speed profile, PSP, and decay rate, DR,correspond to a desired decrease, and rate thereof, of the rotationalspeed of the pump shaft 16 of the torque converter 20 from PS_(C) towardthe turbine shaft rotational speed, TS, such that the actual pump shaftrotational speed, PS, achieves synchronous speed with the turbine shaftrotational speed, TS (i.e., at synchronous speed, PS=TS), with a desireddecreasing pump speed profile and decay rate. In the plot of FIG. 3, forexample, the pump speed profile, PSP, 124 between the pump shaftrotational speed, PS_(C), and synchronous speed 137 (PS=TS) is selectedto be linear (the actual, non-linear pump speed 122 is also shown inFIG. 3 between PS_(C) and synchronous speed, PS=TS), although thisdisclosure contemplates embodiments in which PSP is alternativelypiece-wise linear, or nonlinear. The decay rate, DR, of the pump speedprofile, PSP, will generally be selected to achieve synchronous speed(PS=TS) in a reasonable amount of time after detection of on-comingclutch capacity, taking into account the relative difference betweenPS_(C) and TS as well as the selected profile, i.e., shape, of PSP. Thedecay rate, DR, may be constant or non-constant, and selection of thedecay rate, DR, will generally depend upon the application. In any case,the transmission control circuit 40 is operable at step 214 to selectPSP and DR by retrieving PSP and DR from the memory unit 42. It will beunderstood that the memory 42 may be programmed to store any number ofpump speed profiles, PSP, and corresponding decay rate values, DR, andthe transmission control circuit 40 may then be operable at step 214 toselect the pump speed profile and corresponding decay rate value, or anappropriate one of a plurality of pump speed profiles and correspondingdecay rate value based on one or more pre-established criteria.

The routine 184 advances from step 214 to step 216 where thetransmission control circuit 40 is operable to compute a pumpacceleration profile, PAP, as a function of the pump speed profile, PSP,the pump speed PS_(C) and the decay rate, DR. In embodiments in whichthe pump speed profile, PSP, is linear, for example, PAP will be aconstant value. In other embodiments in which the pump speed profile,PSP, is non-linear, PAP will be a function of time. In any case, theroutine 184 advances from step 216 to step 218 where the transmissioncontrol circuit 40 is operable to begin continually computing PSP andPAP at the decay rate DR. Thereafter at step 220, the routine 184 isreturned to the lockup clutch control routine 116 of FIG. 5.

Referring again to FIG. 5, the routine 116 advances from step 184 tostep 186 where the transmission control circuit 40 is operable todetermine the engine output torque, T_(E), using any one of thetechniques described hereinabove. Thereafter at step 188, thetransmission control circuit 40 is operable to compute a compensatedengine output torque value, T_(EC), as described hereinabove withrespect to step 110 of the process 100. Alternatively, in embodiments inwhich T_(EC) is not computed as described hereinabove, step 188 may beomitted from the routine 116. In any case, the transmission controlcircuit 40 is thereafter operable at step 190 to determine the turbineshaft rotational speed, TS, using any one more of techniques describedhereinabove.

Following step 190, the transmission control circuit 40 is operable atstep 192 to execute an accumulator management routine 192. Referring toFIG. 7, one illustrative embodiment of the accumulator managementroutine 192 is shown. In the illustrative embodiment, the accumulatormanagement routine 192 begins at step 250 where the transmission controlcircuit 40 is operable to determine whether the timer 44 (see FIG. 1) isreset. If so, execution of the routine 192 advances to step 252 wherethe transmission control circuit 40 is operable to determine the currentpump shaft rotational speed, PS, and to set a K^(th) value of the pumpspeed, PS_(K), equal to the current value of the pump shaft rotationalspeed, PS. Thereafter at step 254, the transmission control circuit 40is operable to compute a K^(th) value of pump shaft acceleration, PA_(K)as a function of the current number J, of discrete pump shaft speedvalues, where J may accordingly range from one to the current value ofK.

The routine 192 advances from step 254 to step 256 where thetransmission control circuit 40 is operable to determine whether thecurrent or K^(th) value of the pump shaft acceleration, PA_(K), is lessthan the previous value of the pump shaft acceleration, PA_(k-1).Illustratively, PA₀ is set equal to PA₁, so that step 256 advancesthrough the “NO” branch to step 260 when K=1. If, at step 256, thetransmission control circuit 40 determines that PA_(K) is less thanPA_(K-1), the routine 192 advances to step 258 where the transmissioncontrol circuit 40 is operable to set the value of a minimum pump shaftacceleration variable, PA_(MIN), equal to the current value PA_(K), ofthe pump shaft acceleration. If, on the other hand, the transmissioncontrol circuit 40 determines at step 256 that PA_(K) is greater than orequal to PA_(K-1), execution of the routine 192 advances to step 260where the transmission control circuit 40 is operable to determinewhether the difference PA_(K)−PA_(MIN) is greater than an accelerationthreshold value, A_(th). Illustratively, PA_(MIN) is initially set equalto PA₁ so that execution of step 260 advances to the “NO” branch whenK=1. If, at step 260, the transmission control circuit 40 determinesthat the difference PA_(K)−PA_(MIN) is greater than A_(TH), execution ofthe routine 192 advances to step 262 where the transmission circuit 40is operable to hold PSP and PAP at their current values, i.e., todiscontinue computing PSP and PAP at the decay rate, DR, as describedhereinabove with respect to step 218 of the pump shaft speed andacceleration profile determination routine 184. Following step 262, thetransmission control circuit 40 is thereafter operable at step 264 tostart the timer 244 (see FIG. 1). Following step 264, and also followingstep 258, transmission control circuit 40 is operable at step 256 toincrement the value of K by one.

If, at step 250, the transmission control circuit 40 determines that thetimer 44 is not reset, execution of the routine 192 advances to step 268where the transmission control circuit 40 is operable to determine ifthe current value of the timer is greater than an accumulator detectiontime, T_(AD). If so, the transmission control circuit 40 is thereafteroperable at step 270 to resume determining PSP and PAP at the decay rateDR, i.e. to resume computing PSP and PAP at the decay rate DR inaccordance with step 218 of the routine 184 of FIG. 6. Step 266, the“NO” branch of step 268 and step 270 all advance to step 272 where theaccumulator management routine 192 is returned to step 192 of the lockupclutch control routine 116 of FIG. 5.

Referring again to FIG. 5, the lockup clutch control routine 116advances from step 192 to step 194 where the transmission controlcircuit 40 is operable to compute a lockup clutch torque value T_(LU),as a function of I_(E), T_(EC), PSP, PAP and TS. In one illustrativeembodiment, for example, the transmission control circuit 40 is operableto execute step 194 by computing T_(LU) according to the model:T_(LU)=T_(EC)−T_(P)−(I_(E)*PAP), where T_(P) represents the amount oftorque transmitted by the pump 18 of the torque converter 20 with thepump speed profile, PSP, substituted for actual pump speed.Illustratively, T_(P) is computed by the transmission control circuit 40as a function of PSP and TS using a model-based transmitted torque modelsuch as, but not limited to, that is described hereinabove with respectto step 108 of the process 100. Alternatively, such as in embodiments inwhich the engine output torque value, T_(E), supplied by the enginecontrol circuit 66 to the transmission control circuit 40 via one ormore of the signal paths 64 is not compensated, the transmission controlcircuit 40 may be operable to determine the lockup clutch torque value,T_(LU), according to the model: T_(LU)=T_(E)−T_(P)−(I_(E)*PAP), whereT_(E) represents an uncompensated value of the engine output torque thatmay be determined according to any one or more of the techniquesdescribed hereinabove. In any case, the lockup clutch torque valueT_(LU), computed at step 194 corresponds to the amount of torque thatthe lockup clutch 32 would be transmitting under current operatingconditions if the rotational speed and acceleration of the pump shaft 16of the torque converter 20 were equal to the current values of the pumpspeed profile, PSP, and pump acceleration profile, PAP, respectively.Illustratively, the T_(LU) model is stored in the memory unit 42 of thetransmission control circuit 40, and the transmission control circuit 40is operable at step 194 to retrieve the T_(LU) model from the memoryunit 42, to insert current values of the torque converter operatingparameters I_(E), T_(EC) (or T_(E)), PSP, PAP and TS into the model andto then solve the model equation for T_(LU).

Following step 194, the transmission control circuit 40 is operable atstep 196 to modify the lockup clutch command, LCC, that is used tocontrol the actuator 36 (see FIG. 1) based on the lockup clutch torquevalue, T_(LU), computed at step 194. In the embodiment illustrated inFIG. 1, the lockup clutch command, LCC will typically correspond to alockup clutch pressure command, i.e., a command to which the actuator 36is responsive to establish a corresponding fluid pressure in the fluidconduit 34. In this embodiment, the transmission control circuit 40 isoperable to modify LCC based on T_(LU) by converting T_(LU) from unitsof torque to units of pressure and to then use the converted T_(LU)value as the lockup clutch command, LCC. Illustratively, the lockupclutch torque value, T_(LU), may be converted to a lockup clutchpressure value, P_(LU), according to the equation P_(LU)=T_(LU)*G whereG is a gain value and where P_(LU) then corresponds to a lockup clutchpressure command. It will be understood, however, that this disclosurecontemplates embodiments in which the actuator 36 is responsive to alockup clutch torque command to control the lockup clutch 32 to transmita corresponding torque between the pump shaft 16 and the turbine shaft24. In any case, the transmission control circuit 40 is operable toproduce the lockup clutch command, LCC, as a direct function of T_(LU)computed at step 194 or as a direct substitute of T_(LU) for LCC so thatthe model-based lockup clutch torque value, T_(LU), is used to controloperation of the actuator 36. As it relates to the plot of FIG. 3, thelockup clutch torque, T_(LU), computed at step 194 corresponds to theincreasing pressure portion 136 of the lockup clutch command, LCC, 128between PS_(C) (the intersection of the dashed line 124 and the pumpspeed 122) and a delay time following synchronous speed 137.

The lockup clutch control routine 116 advances from step 196 to step 198where the transmission control circuit 40 is operable to determinewhether synchronous speed has been achieved, i.e., whether PS=TS. Ifnot, execution of the lockup clutch control routine 116 loops back tostep 186. If, on the other hand, the transmission control circuit 40determines at step 198 that PS=TS, execution of the lockup clutchcontrol routine 116 advances to step 200 where the lockup clutchcommand, LCC, is commanded to a full or maximum value, LCC_(MAX), aftera time delay, TD, elapses following the determination that PS=TS.Referring once more to FIG. 3, the lockup clutch command, LCC, 128 isshown as being commanded to LCC_(MAX) 138 when a time delay, TD, elapsesfollowing synchronous speed 137. Following step 200, the lockup clutchcontrol routine 116 is returned at step 202 to the process 100 of FIG.2. Referring once more to FIG. 2, the process 100 loops from step 116back to step 104 for continual execution of the process 100.

In an alternative embodiment, a profile and corresponding rate of changefor another one of the torque converter operating parameters that areincluded in the lockup clutch torque model described in the previousparagraph may be determined and substituted for the pump speed profile,PSP, and decay rate, DR. For example, a turbine speed profile may bedetermined in a manner similar to that described with respect to FIG. 6,and a corresponding increase rate may also be determined wherein theturbine speed profile and corresponding increase rate may be selectedsuch that the turbine speed profile increases over time at a desiredrate so as to thereafter achieve synchronous speed by intersecting withthe pump speed. Alternatively still, a profile and corresponding rate ofchange of another one, or a combination of, the torque converteroperating parameters that are included in the lockup clutch torque modeldescribed above may be determined and substituted for PSP and DR. In anysuch alternative embodiments, the profile may be linear, piece-wiselinear or non-linear, and the corresponding rate of change may beconstant or non-constant. The net effect of artificially modifying oneor more of the torque converter operating parameters to solve for T_(LU)would be the same as in the embodiment illustrated in the FIGS., i.e.,to drive the pump speed 122 to synchronous speed (PS=TS) whilecontrollably modifying LCC as a function of T_(LU) whereby engagement ofthe lockup clutch 32 is continually controlled.

Referring now to FIG. 8, operation of the accumulator management routine192 of FIG. 7 will be described with the aid of the illustrated plotwhich is similar to the plot of FIG. 3. In the plot of FIG. 8, the pumpspeed (PS) 280, pump speed profile (PSP) 282, turbine speed (TS) 284 andlockup clutch command (LCC) 286 are all shown vs. time (seconds). Asdescribed with respect to FIG. 3, the lockup clutch command 286 includesa fill phase in which the lockup clutch command 286 is rapidly increasedto a peak value 290 and then rapidly decreased after a short duration ofthe peak value 290 to an initial lockup clutch activation value 292.Lockup clutch on-coming capacity thereafter occurs, and may be detectedaccording to the lockup clutch on-coming capacity detection routine 114of FIG. 4. In relation to FIG. 8, lockup clutch on-coming capacityoccurs where the dashed line 294 intersects the pump speed 280.

Following detection of lockup clutch oncoming capacity, the lockupclutch command 286 is controllably increased, corresponding to theregion 296 of the lockup clutch command 286, such as in accordance withthe lockup clutch control routine 116 of FIG. 5. It has been observedthat as the lockup clutch command, LCC, is controllably increased, e.g.,in the region 296, such as under the control of the lockup clutchcontrol routine 116 of FIG. 5, a short-duration, e.g., 0.1 seconds,accumulator effect may occur during which increases in the lockup clutchcommand 286 have no effect on the actual pump speed 280, i.e., duringwhich increases in the lockup clutch command 128 do not result incorresponding decreases in the actual pump speed 280. The transmissioncontrol circuit 40 is operable, under control of the accumulatormanagement routine 192, to address such accumulator effects bymonitoring the deceleration rate of the pump shaft 16 after detection oflockup clutch on-coming capacity, comparing the pump shaft decelerationrate to a continually-computed maximum pump shaft deceleration rate, andholding the pump speed profile (PSP) and the pump acceleration profile(PAP) constant for a short time duration, e.g., 200 milliseconds, if thepump shaft deceleration rate rises an acceleration threshold, A_(TH),above the maximum pump shaft deceleration rate. As it relates to thelockup clutch control routine 116, the phrase “holding the pump speedprofile (PSP and the pump acceleration profile (PAP) constant for ashort time duration” means temporarily suspending or discontinuing thecontinual computation of PSP and PAP that was begun at step 218 of thepump shaft speed and acceleration profile determination routine 184 ofFIG. 6, and then resuming the continual computation of PSP and PAP afterthe short time duration has elapsed.

The accumulator management routine 192 is executed after lockup clutchon-coming capacity is detected and during each iteration of the lockupclutch control routine 116. The transmission control circuit 40 isoperable at steps 252-254 to compute pump shaft deceleration, PA_(K), asa function of the “J” most recent pump shaft speed signal samples, whereJ ranges from 1 to K, and where K is a counter for the number ofiterations of the main control loop (between steps 186 and 198) of thelockup clutch control routine 116. Steps 256 and 258 then continuallysearch for and establish the maximum deceleration rate, e.g., whichcorresponds to a minimum value of the pump shaft acceleration (PA_(MIN))since deceleration is generally understood to be negative acceleration.The true maximum pump shaft deceleration rate in the example illustratedin FIG. 8 corresponds to the vertical line 298. Step 260 compares thecurrent pump shaft deceleration value, PA_(K), to the most recentmaximum deceleration rate, PA_(MIN), and if the difference is greaterthan the acceleration threshold, A_(TH), the transmission controlcircuit 40 is operable at steps 262 and 264 to hold PSP and PAP constantand to start the timer 44 (FIG. 1). Step 268 checks the timer 44 andwhen the time value of the timer 44 exceeds the accumulator delay time,T_(AD), the transmission control circuit 40 is operable at step 270 toresume continually computing PSP and PAP as begun at step 218 of thepump shaft speed and acceleration profile determination routine 218. Theend of the accumulator time delay, T_(AD), in the example illustrated inFIG. 8 is indicated by the vertical line 300. In between the verticallines 298 and 300, the pump speed profile 282 (dashed-line) is heldconstant as illustrated in FIG. 8. While the actual pump speed 280 andthe pump speed profile 282 may thereafter deviate as shown, increases inthe lockup clutch command 286 will continue to drive the actual pumpspeed 280 toward the turbine speed 284 until synchronous speed 302 isachieved, after which the lockup clutch command 286 may be increased toits maximum, clutch-engaged value 304.

While the invention has been illustrated and described in detail in theforegoing drawings and description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly illustrative embodiments thereof have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. In a torque converter having a pump that isrotatably driven by an internal combustion engine and that is fluidlycoupled to a turbine, and a lockup clutch connected between pump and theturbine, a method for managing accumulator effects during engagement ofthe lockup clutch, the method comprising: continually solving a dynamicmodel that is configured to produce a lockup clutch command as afunction of a plurality of torque converter operating parameters, theplurality of torque converter operating parameters comprising a pumpspeed, asserting the lockup clutch command to control engagement of thelockup clutch, selecting a profile of one of the plurality of torqueconverter operating parameters that is configured, when inserted intothe model in place of an actual value thereof, to result in anintersection of rotational speeds of the pump and the turbine over time,monitoring deceleration of the pump after asserting the lockup clutchcommand, determining, from monitored values of the deceleration of thepump, a maximum deceleration of the pump, and temporarily holdingconstant the selected profile if the monitored deceleration of the pumprises at least a threshold value above the maximum deceleration of thepump.
 2. The method of claim 1 wherein temporarily holding constant theselected profile comprises holding the selected profile at a constantvalue for a predefined time period following detection of the monitoreddeceleration of the pump rising at least the threshold value above themaximum deceleration of the pump.
 3. The method of claim 1 furthercomprising: monitoring a number of the remaining ones of the pluralityof torque converter operating parameters, and continually solving thedynamic model using the monitored values of the number of the remainingones of the plurality of torque converter operating parameters and theprofile of the one of the plurality of torque converter operatingparameters.
 4. The method of claim 3 wherein the lockup clutch commandcomprises a fill phase followed by an initial lockup clutch activationvalue after which on-coming capacity of the lockup clutch occurs, andwherein the lockup clutch command produced by the model is used tocontrol engagement of the lockup clutch only after the on-comingcapacity of the lockup clutch occurs.
 5. The method of claim 4 whereinmonitoring a number of the remaining ones of the plurality of torqueconverter operating parameters, selecting a profile, continually solvingthe dynamic model using the monitored values of the number of theremaining ones of the plurality of torque converter operating parametersand the profile of the one of the plurality of torque converteroperating parameters, monitoring deceleration of the pump, determining amaximum deceleration of the pump and temporarily holding constant theselected profile are all carried out after on-coming capacity of thelockup clutch occurs.
 6. The method of claim 3 wherein one of theplurality of torque converter operating parameters included in the modelis the inertia of the engine, and wherein selecting a profile comprisesselecting a pump speed profile and computing a pump acceleration profileas a function thereof, the pump speed profile being configured todecrease the rotational speed of the pump from a rotational speed at orjust after on-coming capacity of the lockup clutch occurs to therotational speed of the turbine over time, and wherein monitoring anumber of the remaining ones of the plurality of torque converteroperating parameters comprises monitoring torque applied by the engineto the pump and monitoring rotational speed of the turbine, and whereinthe model defines the lockup clutch command as a function of the inertiaof the engine, the torque applied by the engine to the pump, therotational speed of the turbine, the pump speed profile and the pumpacceleration profile.
 7. The method of claim 6 wherein monitoring torqueapplied by the engine to the pump comprises receiving reported engineoutput torque values produced by a controller configured to controloperation of the internal combustion engine.
 8. The method of claim 6further comprising determining torque transmitted by the pump as afunction of the pump speed profile and the rotational speed of theturbine, wherein the dynamic model defines the lockup clutch commandaccording to the equation:T _(LU) =T _(E) −T _(P)−(I _(E)*PAP), where T_(LU) is the lockup clutchcommand, T_(E) is the torque applied by the engine to the pump, T_(P) isthe torque transmitted by the pump, I_(E) is the inertia of the engineand PAP is the pump acceleration profile.
 9. The method of claim 6wherein monitoring torque applied by the engine to the pump comprises:determining an initial rotational speed of the pump during the fillphase of the lockup clutch command, determining an initial rotationalspeed of the turbine during the fill phase of the lockup clutch command,receiving an initial value of a reported engine output torque producedby a controller during the fill phase of the lockup clutch command,determining a torque offset value as a function of the initialrotational speeds of the pump and the turbine, and the initial value ofthe reported engine output torque, receiving reported engine outputtorque values after on-coming capacity of the lockup clutch occurs, thereported engine output torque values produced by a controller configuredto control operation of the internal combustion engine controller, andcomputing the torque applied by the engine to the pump as a compensatedengine output torque based on the torque offset value and the reportedengine output torque values produced by the controller after on-comingcapacity of the lockup clutch occurs.
 10. The method of claim 9 furthercomprising determining torque transmitted by the pump as a function ofthe pump speed profile and the rotational speed of the turbine, whereinthe dynamic model defines the lockup clutch command according to theequation:T _(LU) =T _(EC) −T _(P)−(I _(E)*PAP), where T_(LU) is the lockup clutchcommand, T_(EC) is the compensated engine output torque, T_(P) is thetorque transmitted by the pump, I_(E) is the inertia of the engine andPAP is the pump acceleration profile.
 11. The method of claim 1 whereinthe lockup clutch command is a pressure command to which a lockup clutchactuator is responsive to control operating pressure of the lockupclutch.
 12. The method of claim 1 wherein selecting a profile of one ofthe plurality of torque converter operating parameters comprises:selecting a linear profile of the one of the plurality of torqueconverter operating parameters, and selecting a change ratecorresponding to a rate of change of the selected linear profile overtime.
 13. The method of claim 1 wherein selecting a profile of one ofthe plurality of torque converter operating parameters comprises:selecting a non-linear profile of the one of the plurality of torqueconverter operating parameters, and selecting a change ratecorresponding to a rate of change of the selected non-linear profileover time.
 14. The method of claim 1 wherein selecting a of one of theplurality of torque converter operating parameters comprises: selectinga pump speed profile that is configured to decrease the rotational speedof the pump from a rotational speed at or just after on-coming capacityof the lockup clutch occurs to the rotational speed of the turbine overtime, and selecting a decay rate corresponding to a rate of decay of theselected pump speed profile over time.
 15. The method of claim 1 whereinselecting a profile of one of the plurality of torque converteroperating parameters comprises: selecting a turbine speed profile thatis configured to increase the rotational speed of the turbine from arotational speed at or just after on-coming capacity of the lockupclutch occurs to the rotational speed of the pump over time, andselecting an increase rate corresponding to a rate of increase of theselected turbine speed profile over time.
 16. In a torque converterhaving a pump that is rotatably driven by an internal combustion engineand that is fluidly coupled to a turbine, and a lockup clutch connectedbetween pump and the turbine, a method for managing accumulator effectsduring engagement of the lockup clutch, the method comprising:continually solving a dynamic model that is configured to produce alockup clutch command as a function of a plurality of torque converteroperating parameters, the plurality of torque converter operatingparameters comprising a turbine speed, asserting the lockup clutchcommand to control engagement of the lockup clutch, selecting a turbinespeed profile that is configured, when inserted into the model in placeof an actual value thereof, to result in an intersection of rotationalspeeds of the pump and the turbine over time, monitoring deceleration ofthe pump after asserting the lockup clutch command, determining, frommonitored values of the deceleration of the pump, a maximum decelerationof the pump, and temporarily holding constant the selected profile ifthe monitored deceleration of the pump rises at least a threshold valueabove the maximum deceleration of the pump.
 17. The method of claim 16wherein temporarily holding constant the selected profile comprisesholding the selected profile at a constant value for a predefined timeperiod following detection of the monitored deceleration of the pumprising at least the threshold value above the maximum deceleration ofthe pump.
 18. The method of claim 16 further comprising: monitoring anumber of the remaining ones of the plurality of torque converteroperating parameters, and continually solving the dynamic model usingthe monitored values of the number of the remaining ones of theplurality of torque converter operating parameters and the profile ofthe one of the plurality of torque converter operating parameters. 19.The method of claim 16 wherein selecting a profile of one of theplurality of torque converter operating parameters comprises: selectinga non-linear profile of the one of the plurality of torque converteroperating parameters, and selecting a change rate corresponding to arate of change of the selected non-linear profile over time.
 20. Themethod of claim 16 wherein selecting a of one of the plurality of torqueconverter operating parameters comprises: selecting a pump speed profilethat is configured to decrease the rotational speed of the pump from arotational speed at or just after on-coming capacity of the lockupclutch occurs to the rotational speed of the turbine over time, andselecting a decay rate corresponding to a rate of decay of the selectedpump speed profile over time.
 21. The method of claim 16 whereinselecting a profile of one of the plurality of torque converteroperating parameters comprises: selecting a turbine speed profile thatis configured to increase the rotational speed of the turbine from arotational speed at or just after on-coming capacity of the lockupclutch occurs to the rotational speed of the pump over time, andselecting an increase rate corresponding to a rate of increase of theselected turbine speed profile over time.